1. Field of the Invention
The present invention relates to dentifrice compositions and more particularly to dentifrice compositions such as toothpastes containing therapeutic agents and/or polishing agents and other ingredients, wherein the composition also contains a controlled amount of alkaline earth metal ion to prevent corrosion and staining when placed in unlined aluminum tubes over extended periods of storage.
2. Description of the Prior Art
Broadly speaking, there are two types of modern day dentifrices on the market which may be described as opaque and clear-gel dentifrice compositions.
Each type of above mentioned dentifrice is marketed under two different versions:
A. Cosmetic Type
B. Therapeutic Type
A cosmetic type toothpaste is one which contains no fluoride and is promoted for whitening and brightening of the teeth. A therapeutic toothpaste, however, contains fluoride as anti-caries agent.
Therapeutic dentifrice compositions such as toothpastes, normally contain a fluoride therapeutic agent such as stannous fluoride, monofluorophosphate, or derivatives thereof, as well as polishing agents, humectants, and other materials. These compositions are usually placed in aluminum or plastic tubes for sale on the commercial market. It is usually preferred to use aluminum tubes but it has been discovered that when such toothpaste compositions contain a therapeutic fluoride compound, a reaction with the interior of the unlined aluminum tube takes place so that staining and other corrosive action occurs apparently because of some reaction or incompatibility between the bare aluminum surface and one or more of the materials in the toothpaste. This incompatibility appears in the form of gas production, swelling of the tube, corrosion, and black stains on the inside surface of unlined aluminum container. Accordingly, the standard practice in the marketing of therapeutic toothpastes today has been to line the aluminum tube with a plastic, lacquer or other material, which therefore substantially adds to the cost of packaging and marketing the toothpaste.
Many prior art attempts have been made to solve this problem because unlined aluminum tubes are much more economical to use and are generally lighter in weight than the lined tubes. For example, U.S. Pat. Nos. 3,662,060 and 3,624,199 disclose compositions which are said to overcome this problem. Further, U.S. Pat. No. 3,678,155 discloses that monofluorophosphate ions prevent corrosion of unlacquered aluminum tubes when the toothpaste contains milled alpha-alumina trihydrates as an abrasive. Also U.S. Pat. No. 3,864,471 discloses a dentifrice composition containing a monofluorophosphate and a polishing agent containing alkaline earth metal carbonate and insoluble alkali metal phosphate, alumina or mixture thereof, to minimize corrosion in unlined aluminum containers.